The taxonomy was standardised using Plants of the World Online (www.plantsoftheworldonline.org/) and the Integrated Taxonomic Information System (https://www.itis.gov/). Obligate aquatics, insectivorous plants, cultivated plants and non-native species are not included in the data set, since their distribution is not primarily controlled by climate. Some pollen types have been combined to a higher taxonomic level because they were not routinely identified across all the sites or because they occurred in too few sites to allow the construction of robust relationships with climate. The pollen data were transformed from raw counts to relative abundance, based on a pollen sum that includes all the taxa in the assemblage.